Lead gallate glasses

ABSTRACT

This invention is directed to the preparation of glasses in the PbO-Ga2O3 field exhibiting good infrared transmitting characteristics out to wavelengths of 8 microns. The binary glasses consist essentially, by weight, of about 15-28% Ga2O3 and 72-85% PbO. However, the preferred glasses contain up to 85% Bi2O3 and consist essentially as included within the area generally encompassed by the curve in FIG. 2.

BACKGROUND OF THE INVENTION

Glasses demonstrating relatively high transmission in the infraredregion of the radiation spectrum are well known in the art. One ratherlarge use of such glasses has been as elements in the construction ofcommercial detection systems based upon sensitivity to heat or infraredradiation.

U.S. Pat. No. 3,723,141 provides a brief review of the prior artdirected to glass compositions asserted to exhibit good infraredtransmission. In general, those prior art glasses had displayed goodtransmittances to wavelengths no longer than six microns and, commonly,no greater than five microns. The patent described glass compositions inthe lead bismuthate system capable of transmitting substantial amountsof infrared radiation at wavelengths longer than six microns. Thoseglasses consisted essentially, expressed in terms of weight percent onthe oxide basis, of

PbO: 10-75

Bi₂ O₃ : 10-85

PbO+Bi₂ O₃ : at least 60

BaO: 2-25

ZnO: 1-10

SiO₂ +B₂ O₃ +P₂ O₅ : <1

Optionally, up to 10% individually and up to 20% collectively of thefollowing oxides may also be present: As₂ O₃, CaO, CdO, GeO₂, HgO, Sb₂O₃, SrO, TiO₂, Tl₂ O₃, the alkali metal oxides, and the colorant ortransition metal oxides. A drawing appended to the patent, whereinpercent transmission is plotted against transmitting wavelengths,indicated a transmittance of at least 50% at a wavelength of 7.5microns, but a rapid loss of transmission at longer wavelengths.

U.S. Pat. No. 3,837,868 is asserted to be an improvement upon theglasses of U.S. Pat. No. 3,723,141, wherein those latter glasses werestabilized to better avoid devitrification through the inclusion of Fe₂O₃. Those glasses consisted essentially, expressed in terms of cationpercent on the oxide basis, of

Bi₂ O₃ : 8-80

PbO: 0-57

CdO: 0-32

PbO+CdO: at least 5%

Fe₂ O₃ : 5-32.5

Optionally, up to 15% total of compatible glassmaking constituents mayalso be present including up to 7.5% BaO and/or ZnO, up to 5% GeO₂, V₂O₅, NiO, CoO, and other transition metal oxides, and up to 2% B₂ O₃+SiO₂.

Rather than repeating the reviews of prior art supplied in thosepatents, the full disclosures of those patents are explicitlyincorporated herein by reference.

SUMMARY OF THE INVENTION

We have discovered a region of glass compositions in the base PbO--Ga₂O₃ system, to which Bi₂ O₃ is preferably included, which can transmitsubstantial infrared radiation to a wavelength of 8 microns and canexhibit refractive indices greater than 2.4. Those glasses have basecompositions consisting essentially, expressed in terms of weightpercent on the oxide basis, of about 72-85% PbO and 15-28% Ga₂ O₃. Theinclusion of Bi₂ O₃ greatly improves the stability of the glassesagainst devitrification and the melting and forming chracteristicsthereof. The chemical durability of these compositions is very good forglasses exhibiting high indices of refraction and infraredtransmissions. They demonstrate no weathering after several months'exposure to ambient environments and do not dissolve when immersed intowater for extended periods at ambient conditions. Moreover, the additionof Bi₂ O₃ dramatically broadens the scope of operable glasscompositions. Thus, Bi₂ O₃ may be incorporated into the glasscomposition in amounts up to 85% and, in so doing, provides glassesdemonstrating the desired infrared transmitting character within thearea generally encompassed by the curve depicted on the ternary diagramcomprising FIG. 1. A somewhat rough approximation of the operableternary compositions consists essentially of

PbO: 10-85

Ga₂ O₃ : 5-30

Bi₂ O₃ : up to 85

The following compatible metal oxides in the indicated individualproportions and collectively in an amount not exceeding about 30% mayalso optionally be present to modify the chemical and physicalproperties of the glass without significantly altering the infraredradiation transmission capability thereof.

    ______________________________________                                        Cs.sub.2 O                                                                             0-20          Rb.sub.2 O                                                                            0-5                                            HgO      0-30          HfO.sub.2                                                                             0-5                                            Tl.sub.2 O.sub.3                                                                       0-20          Al.sub.2 O.sub.3                                                                      0-3                                            Sb.sub.2 O.sub.3                                                                       0-10          ZnO     0-5                                            TeO.sub.2                                                                              0-10          K.sub.2 O                                                                             0-2                                            Cr.sub.2 O.sub.3                                                                       0-5           In.sub.2 O.sub.3                                                                       0-10                                          MnO.sub.2                                                                              0-5           SiO.sub.2                                                                             0-2                                            CuO      0-2           ZrO.sub.2                                                                             0-5                                            CdO      0-12          Nb.sub.2 O.sub.5                                                                      0-5                                            GeO.sub.2                                                                              0-5           Ta.sub.2 O.sub.5                                                                      0-5                                            Na.sub.2 O                                                                             0-2                                                                  ______________________________________                                    

The inclusion of a halogen in an amount up to about 5% is useful inremoving water from the glass and thereby eliminating the strongabsorption in the infrared region of the radiation spectrum at aboutthree microns which is characteristic of water in glass. Chlorineappears to be the most effective of the halogens in this regard. Theapplication of a halogen to reduce the water content of a glass isdisclosed in U.S. Pat. Nos. 3,531,271 and 3,531,306.

PRIOR ART

Inorganic Glass-Forming Systems, H. Rawson, Academic Press, London andNew York, 1967, pages 200-1, furnishes a summary of glass compositionsin the CaO-Ga₂ O₃ system. Increased glass stability was achieved throughthe addition of a few percent of SiO₂.

P. Kantor, A. Revcolevschi, and R. Collongues, "Preparation of IronSesquioxide Glasses by Ultra-Fast Quenching from the Melt ("splatcooling")", Journal of Materials Science, 8, pages 1359-61 (1973)describes the formation of glass bodies of very small size dimensionsthrough splat cooling, i.e., essentially instantaneous cooling. Thus,the products consisted of flakes and/or thin films. The publication wasconcerned principally with compositions in the Fe₂ O₃ --BaO, FeO--CaO,and Fe₂ O₃ --PbO systems, but glasses containing about 40-95 molepercent PbO and 5-60 mole percent Ga₂ O₃ (44.3-95.8 weight percent PbOand 4.2-55.7 weight percent Ga₂ O₃) were noted. Such ranges extend farbeyond the 72-85% PbO/15-28% Ga₂ O₃ regions of the present inventiveglasses, the latter ranges providing commercially practical glassmakingcompositions. Moreover, no physical property data were supplied by theauthors so no indication was furnished of the very high indices ofrefraction and transmission in the infrared portion of the radiationspectrum which are exhibited by the present inventive glasses.

U.S. Pat. No. 3,188,216 is concerned with the preparation of glasseshaving base compositions within the SrO--Ga₂ O₃ system which are capableof transmitting at least 15% of infrared radiation at a wavelength of6.5 microns. The glasses consist essentially of at least 50% by weightof SrO and Ga₂ O₃ in the ratio of 0.66-1.13 parts of Ga₂ O₃ to one partof SrO and optionally contain up to 45% PbO, up to 35% of at least oneoxide selected from the group of Li₂ O, Na₂ O, K₂ O, CaO, and MgO, andup to 40% of at least one oxide selected from the group of CdO, CuO,ZnO, La₂ O₃, TiO₂, ZrO₂, ThO₂, GeO₂, Ta₂ O₅, As₂ O₃, and Sb₂ O₃.Fluoride may replace part of the oxide.

U.S. Pat. No. 3,511,992 discusses the production of a glass consistingessentially of 35 atomic percent germanium, 60 atomic percent selenium,and 5 atomic percent gallium. The glass is stated to demonstrate goodtransmission in the 1-20 micron wavelength regime of the radiationspectrum.

U.S. Pat. No. 4,197,136 is drawn to glasses suitable for use in opticaltransmission lines. The glasses were composed principally of P₂ O₅ andGeO₂, with Ga₂ O₃ being added to dramatically improve their resistanceto attack by water. The patented compositions consisted essentially, inweight percent, of 10-58% P₂ O₅, 15-85% GeO₂, and 5-40% Ga₂ O₃. Nomention is made of the infrared transmission capabilities of theglasses.

U.S. Pat. No. 4,341,542 discloses a method for preparing glassessuitable for use in optical transmission bodies. The method involvesprecipitating an oxide of a glass forming element by the hydrolysisreaction of a halogen compound of said glass forming element in theliquid phase, adding phosphoric acid to the precipitate to producephosphate, removing the water from the phosphate, and then firing thephosphate to vitrify it. Glasses useful in the process were asserted toconsist essentially, in weight percent, of 45-55% P₂ O₅, 20-35% Ga₂ O₃,10-25% GeO₂, and 0-10% SiO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts infrared transmittance curves demonstrated by operableinventive compositions over the range of about 2-8 microns; and

FIG. 2 is a ternary composition diagram of the PbO--Ga₂ O₃ --Bi₂ O₃system illustrating the basic area of glass compositions displaying thedesired infrared transmitting capabilities.

DESCRIPTION OF PREFERRED EMBODIMENTS

Table I reports a number of glass compositions, expressed in terms ofapproximate weight percent on the oxide basis, illustrating theparameters of the invention. PbO, Bi₂ O₃, and Ga₂ O₃ constituted thebatch ingredients therefor, although it will be appreciated that otherstarting materials capable, upon being melted together, of beingconverted into the desired oxide in the proper proportion would besuitable. Because it is not known with which cation(s) the chloride iscombined, it is merely recorded in terms of chloride, in accordance withconventional glass analysis practice. In the following example it wasbatched as lead chloride. Table IA lists the compositions expressed interms of cationic percent.

The batch components were compounded in the appropriate amounts to yield50 grams of glass, the batches ballmilled in a polypropylene jar usingAl₂ O₃ balls, the batches charged into platinum crucibles, and thecrucibles introduced into a furnace operating at 1000° C. After 20minutes, the melts were poured onto a steel plate and the resultantslabs allowed to cool to room temperature in the ambient environment. Avisual description of glass quality is provided in Table I wherein"good" signifies essentially no unmelted batch or devitrificationobserved, "fair" indicates the inclusion of a minor amount of unmeltedbatch or devitrification, and "poor" designates the presence of lessthan 50% glass. Each exemplary composition is positioned in FIG. 2.

In Example 42 dry nitrogen was gently blown across the surface of themelt in order to sweep out the water vapor being volatilized off. Drynitrogen is a very convenient gas for that purpose because, as suppliedcommercially, it is quite dry. Nevertheless, as is explained in U.S.Pat. No. 3,531,271, any gas may be utilized for that function so long asit is dry and is essentially inert to the molten glass. Air, helium, andoxygen are explicitly noted as being operable.

Removal of water from the molten glass can also be effected by bubblinga dry halogen-containing gas through the melt. Dry chlorine and dry HClgases have been disclosed as useful for that purpose.

                                      TABLE I                                     __________________________________________________________________________        1   2   3   4   5   6   7   8   9   10  11  12   13   14                  __________________________________________________________________________    PbO 82  78  74  71  82  71.5                                                                              63.0                                                                              60.5                                                                              66  46  70.5                                                                              63.5 56   51.5                Ga.sub.2 O.sub.3                                                                  18  22  26  29  12  21.5                                                                              29.5                                                                              25.5                                                                              15  12  7.0 12.0 18   21.5                Bi.sub.2 O.sub.3                                                                  --  --  --  --  6   7   7.5 14.0                                                                              19  42  22.5                                                                              24.5 26   27.0                Cs.sub.2 O                                                                    HgO                                                                           Tl.sub.2 O                                                                    In.sub.2 O.sub.3                                                              Cl                                                                            Quality                                                                           Good                                                                              Good                                                                              Good                                                                              Poor                                                                              Fair                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Poor                                                                              Good Good Poor                __________________________________________________________________________        15  16  17  18  19  20  21  22  23  24  25  26   27   28                  __________________________________________________________________________    PbO 59.5                                                                              57.5                                                                              43.5                                                                              48.0                                                                              32.0                                                                              30.5                                                                              28.5                                                                              38.5                                                                              41.5                                                                              37.5                                                                              27.0                                                                              26   22.0 18.5                Ga.sub.2 O.sub.3                                                                  7.0 4.5 18.0                                                                              7.5 21.5                                                                              18.0                                                                              12.0                                                                              9.5 4.5 6.5 6.5 4    9.5  18.0                Bi.sub.2 O.sub.3                                                                  33.5                                                                              38.0                                                                              38.5                                                                              44.5                                                                              46.5                                                                              51.5                                                                              59.5                                                                              52.0                                                                              54.0                                                                              56.0                                                                              66.5                                                                              70   68.5 63.5                Cs.sub.2 O                                                                    HgO                                                                           Tl.sub.2 O                                                                    In.sub.2 O.sub.3                                                              Cl                                                                            Quality                                                                           Good                                                                              Poor                                                                              Good                                                                              Good                                                                              Poor                                                                              Poor                                                                              Good                                                                              Good                                                                              Poor                                                                              Good                                                                              Good                                                                              Poor Good Poor                __________________________________________________________________________        29  30  31  32  33  34  35  36  37  38  39  40   41   42                  __________________________________________________________________________    PbO 17  16.0                                                                              15.5                                                                              11.0                                                                              10.5                                                                              10.0                                                                              6.0 5   40.1                                                                              37.6                                                                              34.4                                                                              37.7 26.2 45.3                Ga.sub.2 O.sub.3                                                                  12  6.5 4.0 9.5 6.5 4.5 11.5                                                                              2   10.5                                                                              9.9 9.0 9.9  15.6 11.9                Bi.sub.2 O.sub.3                                                                  71  77.5                                                                              80.5                                                                              79.5                                                                              83.0                                                                              85.5                                                                              82.5                                                                              93  36.7                                                                              34.3                                                                              31.5                                                                              34.5 50.1 41.4                Cs.sub.2 O                          12.7                                                                              --  --  --   --   --                  HgO                                 --  18.2                                                                              25.1                                                                              --   --   --                  Tl.sub.2 O                          --  --  --  17.9 --   --                  In.sub.2 O.sub.3                    --  --  --  --   8.1  --                  Cl                                  --  --  --  --   --   1.4                 Quality                                                                           Good                                                                              Good                                                                              Poor                                                                              Good                                                                              Good                                                                              Poor                                                                              Fair                                                                              Poor                                                                              Good                                                                              Good                                                                              Good                                                                              Good Good Good                __________________________________________________________________________

                                      TABLE IA                                    __________________________________________________________________________        1   2   3   4   5   6   7   8   9   10  11  12   13   14                  __________________________________________________________________________    PbO 65  60  55  50  70  55  45  45  55  40  65  55   45   40                  Ga.sub.2 O.sub.3                                                                  35  40  45  50  25  40  50  45  30  25  25  25   35   40                  Bi.sub.2 O.sub.3                                                                  --  --  --  --   5   5   5  10  15  35  20  20   20   20                  Cs.sub.2 O                                                                    HgO                                                                           Tl.sub.2 O                                                                    In.sub.2 O.sub.3                                                              Cl                                                                            __________________________________________________________________________        15  16  17  18  19  20  21  22  23  24  25  26   27   28                  __________________________________________________________________________    PbO 55  55  35  45  25  25  25  35  40  35  25  25   20   15                  Ga.sub.2 O.sub.3                                                                  15  10  35  15  40  35  25  20  10  15  15  10   20   35                  Bi.sub.2 O.sub.3                                                                  30  35  30  40  35  40  50  45  50  50  60  65   60   50                  Cs.sub.2 O                                                                    HgO                                                                           Tl.sub.2 O                                                                    In.sub.2 O.sub.3                                                              Cl                                                                            __________________________________________________________________________        29  30  31  32  33  34  35  36  37  38  39  40   41   42                  __________________________________________________________________________    PbO 15  15  15  10  10  10   5   5  33.3                                                                              33.3                                                                              30.8                                                                              33.3 21.1 39.983              Ga.sub.2 O.sub.3                                                                  25  15  10  20  15  10  25   5  21.8                                                                              21.8                                                                              19.2                                                                              21.8 29.8 24.990              Bi.sub.2 O.sub.3                                                                  60  70  75  70  75  80  70  90  29.2                                                                              29.2                                                                              26.9                                                                              29.2 38.6 34.985              Cs.sub.2 O                          16.7                                                                              --  --  --   --   --                  HgO                                 --  16.7                                                                              23.1                                                                              --   --   --                  Tl.sub.2 O                          --  --  --  16.7 --   --                  In.sub.2 O                          --  --  --  --   10.5 --                  Cl                                  --  --  --  --   --    0.042              __________________________________________________________________________

Table II records the annealing point (Ann. Pt.), strain point (Str.Pt.), coefficient of thermal expansion (Coef. Exp.) over the range of25°-200° C. in terms of ×10⁻⁷ /°C., and refractive index (R.I.)determined on several of the exemplary compositions of Table I utilizingmeasuring techniques conventional in the glass art.

                  TABLE II                                                        ______________________________________                                        2         6       21      37   38   39   40   41                              ______________________________________                                        Ann.  375° C.                                                                        383° C.                                                                        --    --   --   --   --   --                            Pt.                                                                           Str.  351° C.                                                                        360° C.                                                                        --    --   --   --   --   --                            Pt.                                                                           Coef. 87.6    83.5    111.3 --   --   --   --   --                            Exp.                                                                          R.I.  2.43    2.21    2.39  2.27 2.45 2.53 2.35 2.31                          ______________________________________                                    

FIG. 1 sets out infrared transmittance curves exhibited by Examples 2,10, and 42. Curve 1 represents Example 2, a binary PbO--Ga₂ O₃composition; Curve 2 designates Example 10, a ternary PbO--Ga₂ O₃ --Bi₂O₃ composition; and Curve 3 illustrates the marked effect which theremoval of water from the glass can have upon the infrared transmissionof the glass. Example 42 represents Example 10 to which chloride wasadded. As is evident from Curve 3, an essentially totally dry glasswould display transmittances in excess of 60% out to wavelengths of 6.5microns and beyond.

Example 10 demonstrated exceptionally good glass quality and so wasselected for further examination. To undertake such examination, a batchappropriate to yield 500 grams of glass was compounded, ballmilled andmelted in platinum crucibles in like manner to the description above.The melt was cast into a graphite mold preheated to 350° C. to produce arectangular slab having dimensions of about 7.5 cm×3 cm×1.3 cm and thisslab annealed at 350° C. The resulting body exhibited a coefficient ofthermal expansion (25°-200° C.) of 111.6×10⁻⁷ /°C., an annealing pointof 319° C., a strain point of 297° C., and a refractive index of2.46±0.05.

We claim:
 1. A stable binary glass exhibiting refractive indices greaterthan 2.4 and infrared transmitting characteristics out to wavelengths of8 microns consisting, expressed in terms of weight percent on the oxidebasis, of about 15-28% Ga₂ O₃ and 72-85% PbO.
 2. A stable ternary glassexhibiting infrared transmitting characteristics out to 8 micronsconsisting essentially, expressed in terms of weight percent on theoxide basis, as included within the area generally encompassed by thecurve in FIG. 2 of about 10-85% PbO, 5-30% Ga₂ O₃, and including Bi₂ O₃in amounts not more than 85%.
 3. An infrared transmitting glassaccording to claim 2 also containing up to 30% total of the followingcomponents in the indicated proportions selected from the group of:

    ______________________________________                                        Cs.sub.2 O                                                                             0-20         Rb.sub.2 O                                                                             0-5                                            HgO      0-30         HfO.sub.2                                                                              0-5                                            Tl.sub.2 O.sub.3                                                                       0-20         Al.sub.2 O.sub.3                                                                       0-3                                            Sb.sub.2 O.sub.3                                                                       0-10         ZnO      0-5                                            TeO.sub.2                                                                              0-10         K.sub.2 O                                                                              0-2                                            Cr.sub.2 O.sub.3                                                                       0-5          In.sub.2 O.sub.3                                                                        0-10                                          MnO.sub.2                                                                              0-5          SiO.sub.2                                                                              0-2                                            CuO      0-2          ZrO.sub.2                                                                              0-5                                            CdO      0-12         Nb.sub.2 O.sub.5                                                                       0-5                                            GeO.sub.2                                                                              0-5          Ta.sub.2 O.sub.5                                                                       0-5                                            Na.sub.2 O                                                                             0-2          Halogen  0-5                                            ______________________________________                                    


4. An infrared transmitting glass according to claim 3 wherein saidhalogen is chloride.